The major goal of the proposed project is to determine the factors which control substrate oxidation in the developing rat ssmall intestine during the suckling, weaning and postewean periods. We will investigate the effects of dietary and naturational changes which occur during these periods of development on intestinal metabolism. An understanding of developing intestinal metabolism and its relation to diet and nutrition is important for providing appropriate nutrition for normal growth and develooment of premature and sick infants. Biochemical studies will be carried out using three tissue preparations; tissue slices, isolated mucosal cells and isolated mitochondria. We will determine the rate of oxidation of glucose, fatty acids, ketone bodies and glutamine by developing rat intestine. We will specifically examine substrate preferences with respect to the weaning process. The interaction of these substrates and their relation to diet and the weaning process will be investigated. We will attempt to differentiate the effects of diet on intestinal metabolism from the effects of cellular and functional changes which occur at the time of weaning. We will induce postweaned intestinal changes by administration of glucocortioids while rat pups are still on a suckling diet. Determination of changes in intestinal metabolism of these rats and comparison to normal controls will better define the effect of diet and developmental changes on intestinal metabolism. A better understanding of the control mechanisms of intestinal metabolism and its relation to mucosal cell absorptive funmction and diet will result from these studies.